1. Field of the Invention
The present invention relates to an ink jet printer and an image printing apparatus having the printer and, more particularly, to an ink jet printer using photo-curing ink which is advantageous to increasing the image printing speed.
2. Description of the Prior Art
An ink jet image printing method of photo-curing type such as ultraviolet curing type can print on various base materials without any dedicated image-receiving layer, and is a technique which receives a great deal of attention mainly for business and industrial purposes. In ultraviolet curing ink jet image printing, an active species is generally produced within a short time by using a high-power light source such as a high-pressure mercury lamp or metal halide lamp, thus promoting ink curing.
In the use of a high-power light source, the ink film characteristic readily degrades after curing, which is unprofitable in terms of power saving and downsizing of the printer. A long time is taken to obtain a printed image by light irradiation on the entire printing surface subsequent to ink jet printing, and the printer inevitably becomes bulky.
To solve this problem, Japanese Unexamined Patent Publication No. 2002-144553 discloses that a printer is so constituted as to follow and irradiate an ink landing position by an ultraviolet light spot guided from an ultraviolet source via an optical fiber, ink can be cured even by a small-output light source, and the image printing speed can also be shortened by almost simultaneously performing ink jet printing and ultraviolet irradiation.
According to the method disclosed in Japanese Unexamined Patent Publication No. 2002-144553, when a serial type on-demand ink jet head is used, the total image printing speed can be increased to a certain degree in correspondence with an increase in ink jet printing speed by executing light spot irradiation in cooperation with head scanning. If a line type on-demand ink jet head advantageous to further increasing the ink jet printing speed is used, an increase in speed is limited due to a restriction by the light spot irradiation speed of ultraviolet rays in mechanically moving the irradiation position.
In recent years, color image printing apparatuses adopt an ink jet printing system which has widely spread for personal use. The ink jet printing system directly prints a color image on a printing sheet, and can print an image without any complicated reversal delivery mechanism for printing images on two sides. The ink jet printing system directly sprays ink from the printing-head to a printing sheet. In order to fix the image, printing sheet and image must be satisfactorily dried. At a portion where printing sheets overlap each other after delivery when images are printed on many printing sheets, drying is insufficient, and images blur (ink transfers or smears) owing to contact between the sheets. This problem is also caused by an additive which is contained in ink in order to prevent nozzle clogging.
To solve this problem, there is proposed the use of ultraviolet curing ink (see, e.g., Japanese Unexamined Patent Publication No. 2001-158865).
There is also proposed an ink jet printer which comprises two printing-heads and increases the speed by coupling U- and 8-shaped convey paths and combining convey procedures and printing orders in double-side printing and single-side printing (see, e.g., Japanese Unexamined Patent Publication No. 2001-328297).
There is also proposed an ink jet printer in which ultraviolet curing ink is used, ultraviolet rays are guided close to a printing-head from an ultraviolet irradiation device via an optical fiber, and an ink landing position on a printing sheet is followed and irradiated to cure ink immediately after each printing (see, e.g., Japanese Unexamined Patent Publication No. 2002-144553).
Japanese Unexamined Patent Publication No. 2001-328297 requires many main driving levers for controlling a printing sheet convey direction. When the printing speed is further increased, control of the main driving levers becomes very cumbersome, generating noise and impairing reliability and durability.
The method in Japanese Unexamined Patent Publication No. 2002-144553 is suitable when the printing-head prints while moving in the main scanning direction (direction perpendicular to the printing sheet convey direction). If printing-heads are linearly arrayed in the main scanning direction and mechanically moved to print in the main scanning direction in order to further increase the speed, ultraviolet rays must be arrayed in the main scanning direction similarly to the printing-heads, greatly increasing the cost.